Devices for the heating of sterile surgical liquids are known in the art. In a wide variety of surgical procedures, sterile fluids are used to irrigate the site of the surgery. It is important that the temperature of the fluids used be strictly controlled. As the portion of the brain that regulates body temperature is shut down with anesthesia, it is important that the introduction of sterile fluids does not cool the body core temperature. Clinical studies have indicated that a range of adverse consequences arise from a change in body core temperature as little as one to three degrees Celsius. The adverse consequences from mild perioperative hypothermia include hypertension and increased vascular resistance, cardiac events, coagulopathy, an increase risk of surgical wound infections, and delays in the body's ability to remove drugs from its systems. An additional potential adverse consequence is shivering which can increase metabolic rate up to 500% and thus increase demands for oxygen and the need to clear carbon dioxide. This list of complications is by no means exhaustive, but it highlights the critical importance in controlling the body core temperature. Careful control of the temperature of sterile irrigation fluids is an important part of controlling body core temperature.
The prior art includes various liquid warming devices to warm sterile fluid. Some are incorporated into a rolling cabinet for placement in a convenient place within the sterile field in an operating room so that sterile fluid is available at an appropriate temperature for uses in the surgery such as irrigation or lavage. It is recognized as desirable that the process for heating the fluid be capable of quickly heating the fluid to bring the fluid to the appropriate temperature. It is also recognized that having the heater apply so much heat that it damages the container used to hold the fluid is undesirable. Use of a heater that can expose personnel to heated surfaces that are hot enough to cause injury is undesirable and in some cases contrary to governmental regulations.
A conventional control system used in the art is shown in FIG. 1. A volume of sterile fluid 108 rests on a sterile drape 110 which in turn rests on an integrated basin 104 in the top of the liquid warming device. The sterile drape 110 thus shields the non-sterile liquid warming device from the sterile field. (One of skill in the art will recognize that the weight of the sterile fluid 108 would cause drape 110 to substantially conform to the shape of the integrated basin 104. These drawings are intended to aid the disclosure of concepts, rather than serve as photographs, thus many gaps will exist in order to highlight the discrete elements.)
The integrated basin 104, the drape 110 and the fluid 108 therein are heated by a heater 112 within the liquid warming device. The heater is controlled by measuring the temperature of the heater with a heater temperature detector 116. A heater controller 120 turns the heater on or provides additional current to cause the heater to heat up further if the measured temperature at the heater temperature detector is below a set point 124. As the temperature of the heater is regulated or controlled independently of the actual current temperature of the fluid in the drape, a participant in the surgery will test the temperature of the fluid by sticking a gloved finger 128 into the sterile fluid. This is somewhat effective as the target temperature for the sterile solution is often close to body temperature. If the fluid feels cool to the gloved finger, an instruction is given directly or indirectly to the controller 120 to increase the set point 124 for the heater. A subsequent gloved finger reaction is used to make additional corrections from time to time.
The temperature of the fluid 108 cannot be precisely predicted based on the set point of the last surgery as the temperature will be affected by the pouring of additional fluid into the drape as the fluid added may not be at the target temperature. The fluid temperature may also vary with changes in the positioning of the liquid warming device closer to airflow in the surgical suite, changes in humidity levels, or other factors. As the gloved finger test is rather subjective, it will give different results based on the person giving the test, the body temperature of the person, the length of time the gloved finger is inserted in the fluid, and other factors.
An additional problem in the prior art relates to maintaining the integrity of the sterile field. The integrity of the sterile field is essential to acceptable outcomes during surgery. Any breach that might indicate that the sterile field has become contaminated is taken very seriously. A breach that is undiscovered for a period of time is especially troublesome as it is difficult to assess when the breach was created and whether it caused the patient to be exposed to contaminants while vulnerable during surgery. Thus, it is no wonder that concerns from breaches in the sterile drapes 110 were taken very seriously. U.S. Pat. No. 6,910,485 for Medical Solution Thermal Treatment System and Method of Controlling System Operation in Accordance with Detection of Solution and Leaks in Surgical Drape Container addresses this concern. Likewise, issued U.S. Pat. No. 6,091,058 for Thermal Treatment System and Method for Maintaining Integrity and Ensuring Sterility of Surgical Drapes Used with Surgical Equipment teaches ways of reducing the risk of damage to surgical drapes from objects placed in the drape covered integrated basin.
Thus, problems associated with the recognized risk of a breach in a sterile drape have led others to develop various ways of reducing this risk or at least quickly detecting the breach.
In order to provide peace of mind to those working in the surgical theater, it would be advantageous to provide a way to use a standard disposable removable container or a freestanding metal container with a sufficiently high structural integrity that could be sterilized.
Plastic basins are one type of container and they are ubiquitous in hospitals and are used in many ways. Plastic basins that are sterilized (for example through irradiation or ethylene oxide gas sterilization) can safely be used in the sterile field without a surgical drape placed over them. Metal basins are currently sterilized and safely reused just as a range of surgical implements are sterilized and reused.
The use of such basins would provide peace of mind as it is difficult to conceive of any activity in the sterile field that could cause a breach in a non-defective plastic or metal basin. A secondary benefit would be that standard gradation marks on the inside walls of the sterile removable basin would provide a visual indication of the amount of sterile fluid remaining in the sterile basin. As using basin gradation marks is done by hospital personnel in other contexts, the use of fluid gradation marks in this context will seem familiar.
One attempt to devise a device for heating fluid that used a substantial disposable basin is described in U.S. Pat. No. 5,129,033 for Disposable Thermostatically Controlled Electric Surgical-Medical Irrigation Bowl and Lavage Liquid Warming Bowl and Method of Use. FIGS. 2A and 2B illustrates the top and side views of the device taught in the '033 patent. A warming bowl 210 contains a heater assembly 234 which in turn contains heater 236, thermostat 238, and temperature indicator 244. The heater assembly 234 rests on support 242 and a passageway to an interior core 230 of the warming bowl 210 with the power supply 222.
The apparatus of FIG. 2 is different from FIG. 1 in that the device of FIG. 2 replaces the occasional measurements by gloved finger with continuous monitoring of the fluid temperature with a thermostat 238 placed in the heater assembly 234.
It appears that the intent of the '033 patent is for the entire assembly including the heater assembly 234, power supply 222, and various controls and indicator lights to be disposable as the '033 patent notes that “[i]rrigation liquid bowls are provided in pre-packaged pre-sterilized form ready for use, and they are non-reusable and disposable, in view of the stringent demands on aseptic conditions and also because of the high cost of reliable sterilization for reusable surgical instruments and accessories.” Disposing of the electronics with the bowl would seem to make this solution prohibitively expensive.
But, it is hard to see a way to sterilize the '033 device as reuse from surgery to surgery would require a method of reliably sterilizing the heater assembly 234 along with the surface of the bowl that would come in contact with the sterile fluid 108. An additional complication is the need to use a sterilization process that does not impair the hermetic seal 240 as an impaired seal would provide a path for contamination of the inner core 230 and subsequent cross-contamination of the sterile fluid for a later surgery with blood products or other contaminants from an earlier surgery.
A second obvious problem with the solution proposed in the '033 patent is that the heater assembly 234 is simply in the way. Placing the heater assembly 234 in the area meant to contain the sterile fluid 108 solved problems for the design engineers but created lasting problems for the surgical staff who must work around the heater assembly 234 so as to avoid imparting a mechanical shock sufficient of causing the components to fail. The staff must also avoid contact with the heater assembly 234 sufficient to cause a breach in the casing of the heater assembly 234 or in the hermetic seal 240 which might allow fluid to contact non-sterilized areas or to adversely effect the electrical operation. Flooding the inner core 230 could be dangerous to surgical staff if the bowl 210 was using power provided through electrical plug receptacle 216 instead of running off batteries 222.
As noted above, even if the risk of causing a failure to the electrical components or seals is slight, such a risk diminishes the peace of mind of the surgical staff. Adding various detectors to quickly detect various failure modes might increase peace of mind somewhat but at yet another set of added costs to the single-use disposable unit.
The prior art lacks a solution for a fluid heating device using a removable container that provides the benefits of using the actual temperature of the sterile fluid as an input to the control system without incurring the risks and problems inherent in the use of such a temperature probe.